Wireless communication systems are being widely deployed in order to provide various kinds of communication services, such as voice or data. In general, the wireless communication system is a multiple access system which can support communication with multiple users by sharing available radio resources. The radio resources can include, for example, time, frequency, codes, and transmission power. The multiple access systems can include, for example, a Time Division Multiple Access (TDMA) system, a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, and a Single Carrier Frequency Division Multiple Access (SC-FDMA) system. Time corresponds to the radio resources in the TDMA system, frequency corresponds to the radio resources in the FDMA system, codes correspond to the radio resources in the CDMA system, and subcarriers and time correspond to the radio resources in the OFDMA system. Furthermore, the wireless communication system is a system supporting bi-directional communication. Such bi-directional communication can be performed using a Time Division Duplex (TDD) mode, a Frequency Division Duplex (FDD) mode, a Half-Frequency Division Duplex (H-FDD) mode or the like. In the TDD mode, uplink transmission and downlink transmission are considered as time resources. In the FDD mode, uplink transmission and downlink transmission are considered as frequency resources. In the HFDD mode, uplink transmission and downlink transmission are considered as a combination of time resources and frequency resources.
The wireless communication system includes a Base Station (hereinafter referred to as a ‘BS’) providing service to a cell (i.e., a specific area). In general, a Mobile Station (hereinafter referred to as an ‘MS’) can communicate with the BS when it is placed within the coverage of the BS. In the case in which the MS is placed at the boundary of the cell or obstacles, such as buildings, exist between the MS and the BS, the quality of communication between the MS and the BS may not be good.
Several methods are being presented in order to extend the coverage of a BS. One of the methods is to introduce a Relay Station (hereinafter referred to as an ‘RS’) to a wireless communication system. The RS can extend the coverage of the BS and improve the rate of cell processing.
Uplink and downlink between a BS and an RS is a backhaul link, and uplink and downlink between a BS and an MS or between an RS and an MS is an access link. Hereinafter, a signal transmitted through the backhaul link is called as a backhaul signal, and a signal transmitted through the access link is called an access signal.
If a large amount of radio resources is assigned in order to transmit backhaul signals between the BS and the RS, the amount of radio resources necessary to transmit access signals between the RS and the MS is insufficient, and the efficiency of radio resources used is lowered.